Extraction and Integration of Mineralogical and Topographic Information Derived from ASTER and DEM Data

Transcription

1 Extraction and Integration of Mineralogical and Topographic Information Derived from ASTER and DEM Data Yasushi Yamaguchi, K. Kurata, R. Hirai (Nagoya Univ.) S. Noda (JOGMEC), and S. Kodama (GSJ) GRSG 28 th Annual Conference Lisbon, Portugal December 2017

2 CONTENTS 1. Introduction 2. Extracting Mineralogical Information 3. Expressing Topography 4. Integration by the HSV Color Model 5. Concluding Remarks

3 ASTER Characteristics High Spatial Resolution 15 m for VNIR bands 30 m for SWIR bands 90 m for TIR bands Wide Spectral Coverage 3 bands in VNIR ( μm) 6 bands in SWIR ( μm) 5 bands in TIR ( μm) Along-Track Stereo Capability B / H 0.6 DEM Elevation accuracy: 15m (3σ) DEM Geolocation accuracy: 50m (3σ) Terra ASTER

4 Objectives Develop a Method to Integrate Spectral Information in Different Wavelength Regions and Topography Easy to Interpret Geologically Integration by Using the HSV Color Model Indices Common methods RGB Color Model This study HSV Color Model Color Images

5 Data Processing Flow ASTER Spectral data Mineralogical information Topography information DEM data Extracting mineralogical information by suppressing the topography effect Orthogonal Transformation Band Ratio + Decision Tree External DEM data Expressing topography information Inverted-slope + Openness Enhancing topography Pan-sharpening Integrating mineralogical and topography information HSV Color Model

6 Integrating Spectral Information and Topography by Using the HSV Color Model Others Carbonate minerals ASTER Data ASTER Data Quartz Clay minerals H: Mineral Type S: Abundance DEM V: Topography Integrated image HSV Color Model Hue (H), Saturation (S), Value (V)

7 CONTENTS 1. Introduction 2. Extracting Mineralogical Information 3. Expressing Topography 4. Integration by the HSV Color Model 5. Concluding Remarks

8 Extracting Mineralogical Information (1) Clay Minerals: Hydrothermal Alteration (2) Chlorite / Epidote / Carbonates (3) Silicate Rocks (4) Iron Oxides Suppressing the topography effect e.g., Band rationing, SAM

9 Clay Minerals: SWIR Response Patterns Reflectance Band4 No significant absorptions Wavelength µm

10 Clay Minerals: SWIR Response Patterns Reflectance Different Patterns in Bands 5, 6, 7 Wavelength µm

11 Clay Minerals: SWIR Response Patterns Reflectance Different Patterns in Bands 5, 6, 7 Wavelength µm

12 Clay Minerals: SWIR Response Patterns Reflectance Different Patterns in Bands 5, 6, 7 Wavelength µm

13 Method : Spectral Indices (Mineral Types) SWIR Patterns Hue Axis-2 Axis-1 (Alu) (Kao) (Mont) Absorption centers shift towards longer wavelengths. Calculate an angle by using the orthogonal transformation. Index = Arctan ( Inner product to Axis-2 Inner product to Axis-1 ) =Angle from Axis 1

14 Hue Image to Show Mineral Types Not in use Not all colors are in use when allocated to Hue(360 ). In use Not in use Axis-2 Axis-1 We can know mineral species, but can NOT know mineral amount.

15 Add Saturation to Show Mineral Abundances Saturation (S): Band ratio to indicate the mineral abundances (Band4) Band5 + Band6 + Band7 Topography Information Suppressed

16 Decision Tree for Chlorite / Epidote / Carbonates - Combining multiple band ratios by the decision tree. - Band ratios can suppress the topography effect. Original Data Ratios among Bands 5-9 Others Clay, Chlorite, Epidote and Carbonates Band 9 / Band 8 Clay Chlorite, Epidote and Carbonates Band 4 / Band 3 Carbonates Bands 6-8 Chlorite Epidote Dolomite Calcite

17 Extracting Chlorite / Epidote / Carbonates Distinguishing between Clay and Chlorite/Epidote Chlorite/epidote have an absorption in band 8 Calcite Dolomite Chlorite Epidote 8 9 Use band 9 / band 8 Alunite 9 8 Kaolinite Montmorillonite 8 Sericite 9 Wavelength (µm)

18 Mapping Chlorite / Epidote / Carbonates H : Mineral Types (Chlorite / Epidote / Carbonates) S : Mineral Abundance by Band Ratios Clay Chlorite/ Epidote Calcite Dolomite 95 Cuprite, Nevada, U.S.A. Chlorite was confirmed in the circled area.

19 CONTENTS 1. Introduction 2. Extracting Mineralogical Information 3. Expressing Topography 4. Integration by the HSV Color Model 5. Concluding Remarks

20 Inverted Slope to Express Topography DEM (Elevation color coding) Slope Image Yajima & Yamaguchi (2014) Bushveld Intrusion in South Africa Slope(deg)= θ tan θ = A / B q A: Elevation (m) B: DEM Grid Size (m) Slope = The maximum slope value in 8 directions Guth(1995) Inverted Slope Image

21 Openness to Express Topography Overground-openness: a quantity to describe sky extent over the point within a certain distance (Yokoyama et al., 1999). Small viewing angle Overgroundopenness Undergroundopenness Mountain Average the angles in 8 directions from a target pixel to the pixel with the smallest viewing angle in each direction.

22 Combining Inverted Slope and Openness Inverted Slope + Openness + Elevation Color Coding 2km

23 Expression of Topography (Plan B) Pan-Sharpening Band 4 is the least affected by mineral absorptions, but its spatial resolution is 30 m. Pan-sharpen by using the VNIR bands with 15 m spatial resolution. Bands 1,2,3 average Weighting of pixels Band The average should be 1.0

24 CONTENTS 1. Introduction 2. Extracting Mineralogical Information 3. Expressing Topography 4. Integration by the HSV Color Model 5. Concluding Remarks

25 Integrating Spectral Information and Topography by Using the HSV Color Model Others Carbonate minerals ASTER Data ASTER Data Quartz Clay minerals H: Mineral Type S: Abundance DEM V: Topography Integrated image HSV Color Model Hue (H), Saturation (S), Value (V)

26 Integrated Image High S More clays Low S Less clays Goldfield Hydrothermal alteration areas were confirmed Cuprite Montmorillonite Clay minerals Kaolinite Alunite Quartz Calcite Other

27 Integrated Image (Plan B) High S More clay Low S Less clay Goldfield Cuprite Goldfield Centre Margin Green Red Montmorillonite Clay minerals Kaolinite Alunite Cuprite Centre Margin Red Green Calcite Other Quartz

28 Concluding Remarks ASTER data are useful to extract mineralogical information. Techniques such as band rationing can suppress the topography effect. Topography was expressed by combining the inverted slope and openness derived from DEM. The HIS color model was employed to integrate mineralogical and topographic information. This technique allows us to provide a color image showing geological information, which can be easily interpreted by a geologist.